Control of oxygen in metals of groups iv-b, v-b, vi-b, and their alloys



CONTROL OF 02 W W. GULLETT YGEN IN METALS OF GROUPS IV-B, V-B, VI-B, AND THEIR ALLOYS Filed Oct. 22, 1958 2 Sheets-Sheet 1 u: i i

I PERCIENT OXYlGEN FIG. 1.

INVENTOR July 5, 1960 GUL W. W. CONTROL OF OXYGEN IN ME IV-B, V-B, VI-B, AND

Filed Oct. 22, 1958 LETT 2,943,984

TALS OF GROUPS THEIR ALLOYS 2 Sheets-Sheet 2 Ema INVENTOR CONTROL OF OXYGEN IN METALS OF GROUPS IV-B, V-B, VI-B, AND THEIR ALLOYS William W. Gnllett, College Park, Md., assignor to Chicago Development Corporation, Riverdale, Md., a corporation of Delaware Filed Oct. 22, 1958, Ser. No. 769,037 1 Claim. 01. 204-1 This is a continuation in part of application, Serial No. 655,834, filed April 29, 1957.

It has for its object the determination of oxygen in solid solution in metals of groups IV-B, V-B and VI-B of the periodic system, that is, Ti, Zr, Hf, Cr, Mo, V, Nb, Ta and W. Particularly it has for its object the provision of a method for determining oxygen in solid solution in said metals without interference from combined oxygen or from the more common impurities such as iron.

I have found that in a specifically defined electrolyte the potential of a cell having an electrode of thepure metal under test and an electrode of the metal containing oxygen in solid solution is a function only of the amount of oxygen in solid solution. The cell potential is related to the percent oxygen in solid solution by the following formula E=A+B log percent :(1)

where E is thecell potential in millivolts, A and B are constants characteristic of the electrolyte and the metal.

,In the following discussion, the applicants explanation of this equation will be set forth; this explanation is, however, not a part of the invention which may be practiced by observing the following procedure:

y (1) Maintain the electrolyte in an inert atmosphere and consisting of at least one molten alkalinous chloridehaving dissolved therein 1-10% of the metal under test as a chloride of mixed valence and alkalinous metal.

(2) Measure the cell potential of the pure metal against at least three samples of the metal containing known oxygen in solid solution.

(3) Determine the constants A and B of the above equation which can readily be done graphically by plotting log percent oxygen against cell potential. In such a plot the intercept on the cell potential axis is A and the slope of the line is B.

It will be clear that having thus determined A and B for the metal and electrolyte being used, we are ready for step 4.

(4) Measure the cell potential of the pure metal against the sample in which oxygen is to be determined. Then calculate the oxygen content for the alloy in which oxygen percent -is to be measured. The constants A and B are determined in the manner heretofore defined and the oxygen percent calculated from Equation 1.

The practice of my invention depends on the specific electrolyte defined herein, in this electrolyte only the oxygen in solid solution has an effect on the cell potential, unless certain unusual impurities are present. Such impurities are Mn, V and Al. When these alloys are present, the measurement of cell potential is made in the same way against an oxygen-free alloy containing the percent of Mn, V or Al respectively.

For the sake of brevity, I will illustrate my invention for the specific case of titanium group metals. It is to be understood, however, that the other metals in groups IV-B, V-B and VI-B behave in an identical manner.

In my application, now abandoned, Serial No. 439,160,

" tent filed June 24, 1954, I have disclosed that the parameter of anode potential in fused'salt electrolytes is a function of. interstitial oxygen content of titanium alloys and that this parameter also controls the response of certain titanium 5 alloys to heat treatment.

My present invention relates to improved methods for measuring the electrode potential of metals containing interstitial oxygen.

I have found that the E.M.l:". generated between two electrodes of a titanium group metal containing different amounts of interstitial oxygen is a definite function of the difference of interstitial oxygen contents.

For convenience, oneof these electrodes may be a titanium group metal containing less than .001% oxygen. The E.M.F. of such a cell is then directly related to the oxygen content.

I have found that the of such a cell isv stable and reproducible if the electrolyte is composed of at least one fused alkalinous metalhalide having dissolved therein 3-5% titanium metal chloride with an average valence of 2.1-2.5 and a significant amount of free alkalinous metal and if said electrolyte is saturated with the dioxide of thetitanium group metal. v V

The electrode reaction is thought to be represented by This requires that the logarithm of the interstitial oxygen content be a linear function of the -E.M.F. and I have found this to be so.

Figure 1 is a curve showing the relation of oxygen content of pure titanium oxygen alloys to the of a cell having one electrode of highly pure titanium (less than .001% oxygen) in an electrolyte like that described above at 1000 C. or entirely in the beta range of the titanium alloys. The oxygen values for this curve were obtained by vacuum fusion analysis and in the case of highly pure titanium these values are accepted as those for interstitial oxygen. :H '5

Example I The of titanium-oxygen alloys were measured in a cell of the following construction (Figure 2): The furnace was circular, 12" in diameter and 9" high; the outer shell 1 was made of steel; and the heating element 2 was a six gauge Nichrome V wire made into a helix 4" in diameter and 5" high which rested against a 4" layer of insulating brick 3. The heating unit radiated directly onto a quartz cell 4 which was 3%" in diameter and 8 /2" high which in turn acted as the container for a glazed porcelain cell 5 in which the measurements were made. The current for operating the heating unit was supplied by low voltage transformer 6 controlled by a heavy duty variable transformer.-

The quartz cell was cemented into a water-cooled flange 7 which was provided with a groove 8 for an O- ring 9. The lid for the cell was of stainless steel six inches in diameter which was fitted with two gate valves 10 and 10 argon inlet 11 and outlet 11 and thermocouple inlet 12. T he electrodes 13 and 14 are introduced to the 0611 through pipes 15 and 15 which are insulated with porcelain tubes '16 and 16 The electrodes are cooled at the top of the pipes 15 and 15 by means of rubber grommets 17 and 17 to allow the maintainance of an inert atmosphere of argon above the electrolyte 18 which had the following composition:

. Patented July 5, 1.950

0.96%; inserted through the in o he molten e ic lv 1 s; set: hich w i ani m of. no kn wn oxygeni ontent; was in A thermocouple was inserted through the thermocouple hole 12 and the electrolyte heated to 900 C. under an atmosphere of argon. The-feleotrode 13, which was a standfll'i t an m electrode with; ygen c ntent: of; nimetan be-I' serted through the second grommet and Pipe andthe electrolyte, .Vibrators 19, 19 were'atfachedlio jthc'top V of the'electrods and theelectrodesIwerelvibrafed during, the measurement of the EMF; Av'oltmetersensitive to .5 mv. was used to record the potential of the. cell The procedure infExample T was used except that the unknown was a sample of zirconium-oxygen alloy in an electrolyte containingi e follow ng composition:

. r '7 V 7 Percent Zirconium insolution 5.0 Zirconium chloride, 21 C1 5 9.8 ZrO 1.0 Na in solution .12

Balance NaCl.

7' The' 'known electrode contained .06% 0 and had 1 6- viously been standardized-against an electrode of very high' purity" zirconiumfcontaining 01% 0 From the E.M.F. value obtained, the per'c'entageof; O' in thenknown sample was determined to be -.02 2%. This corresponded to'a'value of .023% O asdetermined by vacuum fusionanalysis W 1 r Example III The procedure described in Example I was'used eircept i that the unknown sample was composed of fine turnings of titanium-oxygen alloy which were placed in a small perforated iron basket 20, attached'to an iron rod '21. 1 a The basket and rod were inserted through pipe 15 The no n wo 0 .02 se t w sp se n pipe 15 as before. The valuejobtainedworresponded to an oxygen content of 018% as compared to a vacuum fusion analysis of ;020% O repeated with a known sample placed in the perforated steel basket. sample was of identical composition to the material of the otherel'ectrode'ie, .06% 0 An value was" obtained'which was due to thermal effects and was subtracted from the total reading previously V obtained in order to obtain a corrected reading.

'. Wh t isclaimedi The method of determining the content of oxygen upto .06% in solid solution in an electrode selected from the group consisting of a metal'of groups IV-iB, V.-B and VI-B and alloys of these metals with Mn, V and Al, which consists in measuring the of a cell having an electrode selected from a group consisting of the pure 7 metal and an oxygen-free alloy of Mn, V and Al and an electrode of the oxygen solid solution to be measured in a cell with an inert atmosphere having an electrolyte 'consisting essentially of molten sodium chloride having in solution a chloride of mixed valence of the metal andan alkalinous rmretal then calculatingthe percent'oxygen from the equation A+Blog 5 percent O gthe constants A and B having been determined-by measurements with.

the same cell and same electrolyte using metals having known contents of oxygen in s ol-id solution.

References Cited in the tile ofthis pat nt V a UNITED STATES PATENTS 569,722. ,Mon'ow omzo, i896 2,531,747 Steam- .r Nov. 28, 1950 2,744,860 V May 8, 1956 2,817,631 Gu1lett r Mar. 23,1956

In order t eliminate error; 7 ue to hermal in he celLthe procedure *wasthen 

